Mold for casting cylinder blocks of combustion engines

ABSTRACT

A mold for casting cylinder blocks of combustion engines in an upright position includes a cope and a barrel core located therewith for defining a cylinder bore. A drag defines a crank space and is configured for cooperating with the cope to define a cylinder block such that the drag and cope can be stripped in an axial direction with respect to the cylinder bore.

This is a continuation of co-pending application Ser. No. 810,434 filedon Dec. 18, 1985 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to casting and more particularly to amold for casting cylinder blocks of combustion engines.

2. Description of the Prior Art

Cylinder blocks are normally made of grey cast iron or aluminum alloys.With grey cast iron, the external contours of the cylinder block areformed by a mold of compacted molding sand (e.g. green sand comprisingsilica sand, bonding clay, namely bentonite, coal dust and water). Theinternal contours of the cylinder block are formed by means of suitablecores which are made of silica or other types of sand and a cold or hotsetting binder system (resin and catalyst). The cores used in such acasting process are very expensive.

There are two types of such molds in use. The most common mold isdesigned to form a laterally arranged cylinder block through the use ofa cope and drag. The aforesaid cores are assembled into the cope anddrag which are then joined to ready the mold for casting. The mold isstripped in a direction perpendicular to the axes of the cylinder bores.

With the other mold, the cylinder blocks are cast standing upright onthe base area using the aforesaid cores to form the internal contours.The mold halves, which in this particular case are laterally arranged,are also stripped in a direction perpendicular to the axes of thecylinder bores.

The demands of the automobile industry created by the pursuit of weightreduction have resulted in the need for keeping much closer castingtolerances. Unfortunately, the aforesaid casting methods both have thefollowing disadvantages.

The distance deviations between the cope and drag are entirelytransferred to a complete block half thus yielding castings withdifferent wall thicknesses and weight differences.

The crank space of the cylinder block is formed by means of a crankspace core which is considerably more expensive than the green sand usedin the remainder of the mold.

It is difficult to compensate for lifting forces which developespecially in the water-jacket region during the mold filling process.

The methods are necessarily core-intensive which leads to extensive gasproduction during casting and solidification.

SUMMARY OF THE INVENTION

The present invention is directed to a mold for casting cylinder blocksof combustion engines in an upright position. The mold is comprised of acope having a barrel core located therewithin for defining a cylinderbore. A drag defines a crank space without using any cores. The drag isconfigured for cooperating with the cope to define a cylinder block suchthat said drag and cope can be stripped in an axial direction withrespect to the cylinder bore.

The present invention eliminates the disadvantages associated with theprior art. The present invention replaces at least one of the relativelyexpensive cores with moldformed contours. The crank space, for example,may be formed by green sand thus eliminating one of the relativelyexpensive cores. The drag and the cope are designed and arranged toallow the cylinder block to be cast in an upright position. The drag andcope can be stripped from the pattern in an axial direction with respectto the block's cylinder bores. Cylinder blocks cast in molds accordingto the present invention are characterized by closer dimensionaltolerances, generally reduced material consumption, deminishedproduction time, and cost savings.

Because the crank space is formed by green sand, the distances betweenthe cylinder block's bearing supports and their width can hence beproduced with a higher accuracy. It is also possible to provide forlower machining allowances. The nominal wall thickness of the casingwith the surrounding tolerance field can, in comparison withconventionally cast cylinder blocks, be substanially reduced. It is nolonger necessary to support the water-jacket core by chaplets. Due toits upright position, the core is no longer deformed during the castingprocess as is the case with conventional molds where the cylinder blockis arranged in a lateral position. Furthermore, a cylinder bore with acircular outer perimeter is now possible. Said perimeter can thus bedesigned with minimum allowances. In summary, with the mold of thepresent invention, closer manufacturing tolerances coupled with anappreciable weight reduction can be realized.

The external contours of the cylinder block and the crank space can bedesigned without undercuts such that mold halves can be easily strippedin the axial direction. If, however, such undercuts are present, e.g. byreason of design requirements, the undercuts are formed by means ofspecial cores, thus again making vertical mold stripping possible.

It is preferred that the horizontal external parting line between thecope and drag extend horizontally at the level of the base cylinderblock area. With such an arrangement, the influence of distancedeviations between the cope and drag, these deviations being alwayspresent, is completely eliminated. Such an arrangement shouldfurthermore be preferred if the base area represents the lower surfacepart of an outwardly directed flange, which is often arranged at thefree end of the crank space wall to serve as a connecting area for theengine's oil body. Regarding the position of the horizontal parting linebetween the mold halves, it can generally be said that it may extendabove the base area level provided that the principle of axial strippingis maintained and it is not necessary to eliminate those disadvantageswhich will arise by the inevitably present distance deviations betweenthe mold halves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a first design version of a known moldwith a horizontal parting line;

FIG. 2 illustrates schematically a second known mold with a verticalparting line;

FIG. 3 illustrates schematically a mold constructed according to thepresent invention, designed without undercuts, and having a horizontalouter parting line; and

FIG. 4 illustrates schematically a partial section of a mold constructedaccording to the present invention with a horizontal outer parting lineand with undercuts formed by means of cores.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It should be mentioned that the mold designed according to the presentinvention for casting cylinder blocks of combustion engines is generallyapplicable to cylinder blocks of passenger cars, trucks, vessel drives,etc. In the following, the present invention is discussed in detailbased on a preferred embodiment thereof, from which further importantfeatures are derived. However, in order to elucidate the advantages ofthe present invention, the aforesaid known conventional molds are shownin FIGS. 1 and 2 and described hereinafter.

The known mold shown in FIG. 1 comprises a drag 1, a cope 2, a crankspace core 3, a head face slab barrel core 4, and a water-jacket core 5.A parting line 6 between the mold halves 1, 2 extends verticallycoinciding with the longitudinal axis of the cylinder block 7 to becast.

The external contour 8 of the cylinder block has some projections in theradial direction thus making axial mold stripping impossible. The moldhalves 1, 2 are therefore stripped from the pattern in the radial, i.e.horizontal direction, as indicated by arrow 9.

The well-known mold shown in FIG. 2 is basically designed according tothe principle shown in FIG. 1, but with the cylinder block to be cast inan upright position being the sole deviation from FIG. 1. In FIG. 2 themold halves are also stripped in the radial direction, i.e. in thedirection indicated by arrow 9.

The mold according to the present invention shown in FIG. 3 comprises adrag 11, a cope 12, a head face slab barrel core 13 and a water-jacketcore 14. The drag 11 takes over the function of the crank space core 3illustrated in FIGS. 1 and 2. A parting line 15 between the mold halves11, 12 extends horizontally along the external mold sides namely at thelevel of the base area of the cylinder block 16. Inwardly adjacent tothat, the parting line 15 follows the crank space contour. It is evidentthat the external contour 17 of the cylinder block does not reveal anyundercuts. Thus the mold halves 11, 12 can be stripped axially in thedirection indicated by arrow 18. (The axis is indicated as 19 in FIG.3).

It is also evident that the crank space does not include undercuts, sothe drag 11 can be stripped in a downward direction without encounteringany obstacles.

Because the normally available crank space core is eliminated, beingreplaced by the green sand of the drag 11, the gas evolution, whichwould otherwise take place due to the resin binder decomposition causedby the heat in the crank space core during the casting process, issubstantially reduced. Furthermore, the walls throughout the entireblock can repetitively be produced within dimensional tolerances, aresult not realizable hitherto.

The mold according to the invention shown in FIG. 4 correspondsessentially to that one shown in FIG. 3.

In FIG. 4, the crank space and the external contour are substantiallycreated by the green sand mold. Undercuts are formed by the cores 20, 21which are assembled into the drag and/or cope 11, 12, respectively. Ataper 22 exists between the cope 12 and the core 21 which forms, withrespect to the axis 19, an acute, downwardly opening angle. This taper,together with the radii 23 on the shoulders of the drag 11 and on thecore 22, facilitate stripping the mold in the direction indicated byarrow 18.

What is claimed is:
 1. A mold for casting a cylinder block for acombustion engine in an upright position, comprising:a cope; a waterjacket core located within said cope for defining a cooling passage; ahead face barrel core located within said cope for defining cylinderbores; and a drag defining, without cores, a crank space, said dragconfigured for cooperating with said cope to define a parting planetherebetween, said plane extending substantially radially outward withrespect to said cylinder bores, said drag and cope further defining acylinder block such that said drag and cope can be stripped axially withrespect to said cylinder bores.
 2. The mold of claim 1 wherein one ofsaid cope and said drag defines a base of the cylinder block, andwherein said parting plane extends substantially radially atsubstantially the same level as that of said base of the cylinder block.3. The mold of claim 1 additionally comprising an undercut core locatedwithin said cope for defining an undercut in the cylinder block.
 4. Themold of claim 1 wherein said undercut core is tapered to form, withrespect to an axis of the cylinder bores, and acute angle openingdownwardly thereby facilitating axial stipping of said cope.
 5. A methodfor providing a mold for casting a cylinder block for a combustionengine in an upright position, said method comprising the stepsof:providing a cope; locating a water jacket core within said cope fordefining a cooling passage; locating a head face barrel core within saidcope for defining cylinder bores; and providing a drag defining, withoutcores, a crank space, said drag being configured for cooperating withsaid cope to define a parting plane therebetween, said plane extendingsubstantially radially outward with respect to said cylinder bores, saiddrag and cope further defining a cylinder block such that said drag andcope can be stripped axially with respect to said cylinder bores.